1. Field of the Invention
In making decorative laminates, a plurality of sheets are impregnated with a thermosetting resin and stacked in superimposed relation with a decorative sheet placed on top.
The assembly is then heat and pressure consolidated. Generally, more than one laminate is formed at one time by inserting a plurality of assembled sheets in a stack with each assembly being separated by a release sheet which allows the individual laminates to be separated after heat and pressure consolidation.
The laminates so formed are then bonded to a substrate such as plywood, hardboard, asbestos board, particle board, and the like by the use of adhesives such as contact adhesives, urea-formaldehyde, white glues (polyvinyl acetate emulsions), hot melts, phenolic or resorcinolformaldehyde, epoxy, coal tar, animal glues and the like.
Before the laminate can be applied to its supporting substrate, it must be first sanded on its back most surface. This is because conventionally used adhesives will not directly adhere to the phenolic impregnated in the back sheet. In addition, the release medium separating the laminates, has some of the release material on its surface transfer to the back surface of the laminate. By back most surface, it is meant to refer to the exposed flat surface of the lamina which is furthest away from the decorative sheet.
The sanding operation is an expensive step in the process and adds to the cost of the product. While the use of contact adhesives avoids this problem to a certain extent, the expense involved in using such adhesives together with the fact the laminate manufacturer can not predict what type of adhesive will be used, makes sanding a standard step in laminate manufacture. The sanding operation has an additional shortcoming where exceedingly thin laminates are made as the laminates frequently become damaged during the sanding operation because of their extreme thinness. This results in rejects.
For a considerable period of time, the laminating industry has been seeking some method of perfecting a technique that would allow the manufacture of a decorative laminate capable of directly adhering, without a sanding operation, to a supporting substrate by use of conventional low priced adhesives.
2. Prior Art
The only known pertinent prior art is U.S. Pat. No. Re. 27,644 which issued to Peter Barnard Kelley et al wherein the back surface of a decorative laminate is coated with a polyvinyl acetate composition. This coating delaminates with moderate temperature fluctuation and does not in practice serve as a glue line for urea-formaldehyde and phenol resorcinol which are two of the most commonly used adhesives for securing a laminate to a supporting substrate.